spring security自定义配置类继承WebSecurityConfigurerAdapter，一般会配置开放接口、登录接口以及自定义的过滤器等

// 这里我配置了登录成功后返回json数据，但并没有效果，仍然跳转到默认路径/
http
     .formLogin()
     .successHandler(
	     (request, response, authentication) -> {
	            CustomUser principal = (CustomUser) authentication.getPrincipal();
	            response.setCharacterEncoding("utf-8");
	            response.setContentType("application/json;charset=utf-8");
	            PrintWriter out = response.getWriter();
	            out.write(JSON.toJSONString(ResultVo.SUCCESS(JwtUtils.generateJsonWebToken(principal))));
	            out.flush();
	            out.close();
	        }
		)

走进successHandler()方法看到，该方法位于AbstractAuthenticationFilterConfigurer类中

public abstract class AbstractAuthenticationFilterConfigurer<B extends HttpSecurityBuilder<B>, T extends AbstractAuthenticationFilterConfigurer<B, T, F>, F extends AbstractAuthenticationProcessingFilter> extends AbstractHttpConfigurer<T, B> {
    private F authFilter;
    private AuthenticationDetailsSource<HttpServletRequest, ?> authenticationDetailsSource;
    private SavedRequestAwareAuthenticationSuccessHandler defaultSuccessHandler;
    private AuthenticationSuccessHandler successHandler;
    private LoginUrlAuthenticationEntryPoint authenticationEntryPoint;
    private boolean customLoginPage;
    private String loginPage;
    private String loginProcessingUrl;
    private AuthenticationFailureHandler failureHandler;
    private boolean permitAll;
    private String failureUrl;

    protected AbstractAuthenticationFilterConfigurer() {
    // 这里面定义了默认的登录成功处理SavedRequestAwareAuthenticationSuccessHandler
        this.defaultSuccessHandler = new SavedRequestAwareAuthenticationSuccessHandler();
        this.successHandler = this.defaultSuccessHandler;
        this.setLoginPage("/login");
    }

    public final T defaultSuccessUrl(String defaultSuccessUrl) {
        return this.defaultSuccessUrl(defaultSuccessUrl, false);
    }

    public final T defaultSuccessUrl(String defaultSuccessUrl, boolean alwaysUse) {
        SavedRequestAwareAuthenticationSuccessHandler handler = new SavedRequestAwareAuthenticationSuccessHandler();
        handler.setDefaultTargetUrl(defaultSuccessUrl);
        handler.setAlwaysUseDefaultTargetUrl(alwaysUse);
        this.defaultSuccessHandler = handler;
        return this.successHandler(handler);
    }

   ...

	// 自定义成功处理调用这个方法，都是设置successHandler
    public final T successHandler(AuthenticationSuccessHandler successHandler) {
        this.successHandler = successHandler;
        return this.getSelf();
    }

}

可以看出这个类是认证过滤器配置类，因为我后面还配置了自定义的登录过滤器，所有会不会是后面配置的过滤器把上面的配置覆盖掉了

public class AuthenticationProcessingFilter extends UsernamePasswordAuthenticationFilter {

    /**
     * json格式登录
     * @param request
     * @param response
     * @return
     * @throws AuthenticationException
     */
    @Override
    public Authentication attemptAuthentication(HttpServletRequest request, HttpServletResponse response) throws AuthenticationException {
        if (request.getContentType().equals(MediaType.APPLICATION_JSON_VALUE)) {
            ObjectMapper mapper = new ObjectMapper();
            UsernamePasswordAuthenticationToken authRequest = null;
            try (InputStream is = request.getInputStream()) {
                Map<String, String> authenticationBean = mapper.readValue(is, Map.class);
                authRequest = new UsernamePasswordAuthenticationToken(authenticationBean.get("username"), authenticationBean.get("password"));
            } catch (IOException e) {
                e.printStackTrace();
                authRequest = new UsernamePasswordAuthenticationToken("", "");
            }
            setDetails(request, authRequest);
            return this.getAuthenticationManager().authenticate(authRequest);
        } else {
            return super.attemptAuthentication(request, response);
        }
    }

}

这里继承UsernamePasswordAuthenticationFilter ，重写的认证方法，走进UsernamePasswordAuthenticationFilter 发现他继承AbstractAuthenticationProcessingFilter

public abstract class AbstractAuthenticationProcessingFilter extends GenericFilterBean implements ApplicationEventPublisherAware, MessageSourceAware {
    protected ApplicationEventPublisher eventPublisher;
    protected AuthenticationDetailsSource<HttpServletRequest, ?> authenticationDetailsSource = new WebAuthenticationDetailsSource();
    private AuthenticationManager authenticationManager;
    protected MessageSourceAccessor messages = SpringSecurityMessageSource.getAccessor();
    private RememberMeServices rememberMeServices = new NullRememberMeServices();
    private RequestMatcher requiresAuthenticationRequestMatcher;
    private boolean continueChainBeforeSuccessfulAuthentication = false;
    private SessionAuthenticationStrategy sessionStrategy = new NullAuthenticatedSessionStrategy();
    private boolean allowSessionCreation = true;

	// 他里面也定义的这个SavedRequestAwareAuthenticationSuccessHandler
	// 我上面配置的SuccessHandler没有生效，可能是他走的是这个
    private AuthenticationSuccessHandler successHandler = new SavedRequestAwareAuthenticationSuccessHandler();
    private AuthenticationFailureHandler failureHandler = new SimpleUrlAuthenticationFailureHandler();

	...

	// 这里面也有一个设置SuccessHandler的方法
    public void setAuthenticationSuccessHandler(AuthenticationSuccessHandler successHandler) {
        Assert.notNull(successHandler, "successHandler cannot be null");
        this.successHandler = successHandler;
    }
}

然后我就在配置类中添加过滤器的地方设置successHandler

	@Bean
    public AuthenticationProcessingFilter authenticationProcessingFilter() throws Exception {
        AuthenticationProcessingFilter authenticationProcessingFilter = new AuthenticationProcessingFilter();
        authenticationProcessingFilter.setAuthenticationManager(authenticationManagerBean());
        // 设置successHandler 
        authenticationProcessingFilter.setAuthenticationSuccessHandler(authenticationSuccessHandler());
        return authenticationProcessingFilter;
    }
    
	@Override
    protected void configure(AuthenticationManagerBuilder auth) {
        auth.authenticationProvider(adminAuthenticationProvider());
    }

    /**
     * 自定义认证
     * @return
     */
    @Bean
    public AdminAuthenticationProvider adminAuthenticationProvider() {
        return new AdminAuthenticationProvider();
    }

@Bean
    public AuthenticationSuccessHandler authenticationSuccessHandler() {
        return (request, response, authentication) -> {
            CustomUser principal = (CustomUser) authentication.getPrincipal();
            response.setCharacterEncoding("utf-8");
            response.setContentType("application/json;charset=utf-8");
            PrintWriter out = response.getWriter();
            out.write(JSON.toJSONString(ResultVo.SUCCESS(JwtUtils.generateJsonWebToken(principal))));
            out.flush();
            out.close();
        };
    }

这样设置就可以了。总结：当添加过滤器时，在过滤器中设置AuthenticationSuccessHandler，而不要在http.formLogin()后面设置